Metering device for a nozzle of a hot runner injection molding apparatus

ABSTRACT

An injection molding apparatus includes an injection piston that is slidable within a nozzle having a movable valve gate pin. The injection piston is movable from a retracted position to an extended position in order to force melt towards a mold cavity. A valve is located at a forward end of the piston to selectively block communication between a recess, which is provided in an outer wall of the piston adjacent the valve, and a melt chamber of the nozzle. Movement of the injection piston from the retracted position to the extended position causes the valve to close so that the predetermined volume of melt located below the valve is forced into the mold cavity, when the valve gate pin opens the mold gate.

This application is a continuation of Ser. No. 10/245,723 filed Sep. 18,2002, now U.S. Pat. No. 6,884,061.

FIELD OF THE INVENTION

The present invention relates generally to an injection moldingapparatus, and in particular to a metering device for a hot runnernozzle, which injects a predetermined quantity of melt into a moldcavity.

BACKGROUND OF THE INVENTION

In an injection molding apparatus, a manifold receives a pressurizedmelt stream from a machine nozzle. The manifold distributes the meltstream to a plurality of nozzles and the melt is forced through thenozzles and into a plurality of mold cavities. The melt is then cooledin the mold cavities and the molded parts are released so that anothercycle can begin.

The amount of melt transferred to each nozzle can vary due to effectssuch as shear induced flow imbalance in the manifold, for example. Inorder to compensate for such effects and ensure that a sufficient amountof melt is delivered to each mold cavity, the pressure applied to themelt stream by the machine nozzle must be very high. For applicationssuch as injection molding of thin walled vessels and micro-molding, evenhigher nozzle pressures are required in order to produce quality moldedproducts. As a result, the machine nozzle must be very large in order togenerate sufficient pressure to properly distribute the melt to the moldcavities. In many cases, however, increasing the size of the machinenozzle is not a practical solution. Alternative solutions for increasingthe pressure generated in each individual nozzle are thereforedesirable.

Precise measurement of the volume of melt transferred in each shot forthin walled molded parts and micro-molded parts is also very important.This presents a unique challenge particularly when dealing with micromolded parts, which typically weigh a fraction of a gram. Several priorart devices have been developed to control the volume of melt that isinjected into a mold cavity. These devices have typically been employedwhen injecting more than one material into a single mold cavity and tendto be complex and costly to manufacture.

U.S. Pat. No. 5,112,212 to Akselrud et al. discloses a shooting pot,which is used as a metering device, for use in a co-injection moldingapparatus. The shooting pot is located remote from the hot runner nozzleand is used to control the volume of one of the two molten materialsinjected into the cavity. The shooting pot includes a piston that isaxially movable within a cylinder to force molten material from thecylinder into a nozzle, which leads to a mold cavity. The cylinderincludes an inlet that delivers melt from a melt source to a reservoir,which is located in a lower end of the piston. The piston is rotatableto move the reservoir out of communication with the inlet to seal it offso that when the piston is lowered, a known volume of melt is forcedinto the mold cavity.

U.S. Pat. No. 4,863,369 to Schad et al. discloses an injection moldingapparatus that uses a shooting pot to deliver a precisely measuredquantity of melt to a mold cavity. A valve is located in a conduitbetween a melt source and each nozzle. Once the shooting pot and nozzleare filled with melt, the valve is closed and the mold gate is opened. Apiston of the shooting pot advances until it bottoms out in a cylinderto deliver a precise quantity of melt to a mold cavity.

A disadvantage of shooting pots that are remotely located from thenozzle and the mold cavity is that the known or measured volume of meltmay vary from one molding cycle to the next. This occurs because thereis a large volume of melt that is located between the shooting pot andthe mold cavity i.e. the melt in the nozzle, the melt in the manifoldchannel and the melt in the shooting pot. This large volume of meltintroduces several variables. Minor deviations in temperature orpressure, for example, may result in significant variations of the knownvolume. The sizable distance between the shooting pot and the moldcavity further causes the melt to have a long residence time outside ofthe nozzle between the injection of one article to the next. Thisresults in molded parts that are not of the highest quality because thetemperature of the melt coming from the shooting pot may be either underheated or over heated.

It is therefore an object of the present invention to provide a meteringdevice for a nozzle of an injection molding apparatus, which obviates ormitigates at least one of the above disadvantages.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided aninjection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream ofmoldable material under pressure, the manifold channel having an outletfor delivering the melt stream to a nozzle channel of a nozzle;

a mold cavity receiving the melt stream from the nozzle, the nozzlechannel communicating with the mold cavity through a mold gate;

a gating mechanism for selectively closing the mold gate;

a piston extending through the nozzle channel of the nozzle and beingslidable therethrough, an outer wall of the piston abutting an innerwall of the nozzle channel, the piston being movable from a retractedposition to an extended position to force melt towards the mold cavity;

a valve located at a forward end of the piston, the valve beingselectively movable to block communication between a recess, which isprovided in the outer wall of the piston adjacent the valve, and a meltchamber of the nozzle channel, the valve being open to allow melt toflow from the manifold channel into the recess and into the melt chamberof the nozzle channel when the piston is in the retracted position;

wherein movement of the piston towards the extended position forces meltlocated in the melt chamber of the nozzle channel to flow into the moldcavity.

According to another aspect of the present invention there is provided amethod for forcing melt into a mold cavity of an injection moldingapparatus, the method comprising:

-   -   closing a mold gate of the mold cavity to block a melt stream        from flowing from a nozzle channel of a nozzle into the mold        cavity;

maintaining a piston located in the nozzle channel in a retractedposition, in which a valve located at a forward end of the piston isopen to enable the melt stream to flow from a manifold channel of amanifold, through a recess provided adjacent the forward end of thepiston into a melt chamber of the nozzle channel, to fill the nozzlechannel with melt;

closing the valve to block flow of the melt stream between the recessand the melt chamber of the nozzle channel;

opening the mold gate; and

moving the piston towards an extended position to force the melt locatedin the melt chamber of the nozzle channel into the mold cavity.

According to another aspect of the present invention there is provided apiston for a nozzle of an injection molding apparatus comprises:

a valve located on a forward end of the piston, the valve beingselectively closable to block communication between a-recess, which isprovided in the outer wall of the piston adjacent the valve, and a meltchamber of a nozzle channel; and

wherein the valve is open to allow melt to flow from the recess past thevalve when the piston is in a retracted position and the valve is closedwhen the piston is moved toward an extended position in order to forcemelt into a mold cavity.

According to yet another aspect of the present invention there isprovided an injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream ofmoldable material under pressure, the manifold channel having an outletfor delivering the melt stream to a nozzle channel of a nozzle;

a mold cavity receiving the melt stream from the nozzle channel, thenozzle channel communicating with the mold cavity through a mold gate;

a gating mechanism for selectively closing the mold gate;

a melt chamber located in the nozzle channel adjacent the mold gate, themelt chamber having a predetermined volume;

a valve located between the outlet of the manifold channel and the meltchamber, the valve being selectively movable to control melt flow fromthe manifold channel into the melt chamber; and

wherein the predetermined volume of melt is injected into the moldcavity in a single shot.

According to still another embodiment of the present invention there isprovided a method of injecting a predetermined volume of a moltenmaterial into a mold cavity comprising:

-   -   a) injecting molten material through a hot runner manifold into        a valve gated hot runner nozzle including a movable valve pin,        where the valve pin is in the closed position engaging a mold        gate;    -   b) opening the mold gate;    -   c) injecting the molten material into a mold cavity through the        mold gate by moving an injection piston located at least        partially in the nozzle to transfer the predetermined volume of        molten material from the hot runner nozzle into the mold cavity.    -   d) closing the communication between the hot runner nozzle and        the mold cavity by moving the valve pin into engagement with the        mold gate.

According to another embodiment of the present invention there isprovided a method of injecting a predetermined volume of a moltenmaterial into a mold cavity comprising:

-   -   a) injecting molten material through a hot runner manifold into        a valve gated hot runner nozzle including a movable valve pin,        where the valve pin is in the closed position engaging a mold        gate;    -   b) blocking communication between the hot runner manifold and        the hot runner nozzle;    -   c) opening the mold gate;    -   d) moving an injection piston located at least partially in the        nozzle toward the mold gate to transfer the predetermined volume        of molten material from the hot runner nozzle into the mold        cavity;    -   e) closing the communication between the nozzle and the mold        cavity by moving the valve pin into engagement with the mold        gate.

The present invention provides an advantage in that a metered quantityof melt is delivered consistently to a mold cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings.

FIG. 1 is a side sectional view of an injection molding apparatus of thepresent invention.

FIG. 2 is a side sectional view of a valve of a piston of FIG. 1.

FIG. 3 is a view on 3—3 of FIG. 2.

FIG. 4 is a view on 4—4 of FIG. 3.

FIGS. 5 to 9 are schematic side views of a portion of FIG. 1 atdifferent stages of the injection cycle.

FIG. 10 is a schematic side sectional view of another embodiment of aninjection molding apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, portions of a hot runner injection moldingapparatus are generally shown at 10. The injection molding apparatus 10comprises a manifold 12 having a manifold melt channel 14 for receivinga melt stream of moldable material under pressure from a manifoldbushing 16. Manifold 12 is positioned between a back plate 41 and a moldcavity plate 31, such that manifold bushing 16 extends through backplate 41 and is in communication with a machine nozzle of an injectionmolding machine (not shown). Bores 20 extend through the manifold 12 atdistal ends of the manifold melt channel 14. The bores 20 are incommunication with the manifold melt channel 14 and extend generallyperpendicular thereto.

Hot runner nozzles 18 are coupled to a lower surface of the manifold 12and are positioned within nozzle bores 29 in mold cavity plate 31 suchthat an insulative air space 32 is provided between hot runner nozzles18 and mold cavity plate 31. A nozzle channel 22 of each nozzle 18 isaligned with a respective bore 20 to receive the melt stream of moldablematerial from the manifold 12. A mold gate 24 is located adjacent anozzle tip of each nozzle 18. The mold gates 24 are openable to allowdelivery of the melt stream to respective mold cavities 26 that arerespectively formed between mold cavity plate 31 and movable mold cores33. Any number of nozzles 18 can be used to feed either a single or aplurality of mold cavities 26. The mold cavities 26 may be of the samesize and shape or they may differ. Manifold heaters (not shown) andnozzle heaters (not shown) maintain the melt stream at a desiredtemperature and cooling channels (not shown) within mold cavity plate 31facilitate cooling of the mold cavities 26.

A metering device in the form of a hot runner injection piston 40 isslidable through the bore 20 of the manifold 12 and the nozzle 18. Avalve pin 28 extends through a central bore 42 of the injection piston40 and is slidable therethrough to open and close the mold gate 24. Theinjection piston 40 and the valve pin 28 are driven independently andmove relative to one another. The valve pin 28 is pneumatically drivenby a valve piston 30 that is slidable in a cylinder 34. The injectionpiston 40 is pneumatically driven by a second piston 44 that is slidablein a second cylinder 46. The injection piston 40 and valve pin 28 arenot limited to being driven pneumatically, they may be also drivenhydraulically or by any other suitable means, including electrical andelectromagnetic motors. In addition, the valve pin 28 may be replaced byanother type of gating mechanism.

The injection piston 40 further comprises a piston body 50 that extendsoutwardly from the second piston 44. The piston body 50 is coupled tothe second piston 44 by fasteners (not shown). Alternatively, the pistonbody 50 may be integral with the piston 44. The piston body 50 includesan outer surface 51, which blocks the communication between the manifoldchannel 14 and the nozzle channel 22 during movement of the piston body50 towards the mold cavity 26. An annular recess 48 is provided in theouter surface 51 of the piston body 50. It will be appreciated that theannular recess 48 need not extend around the entire circumference of theouter surface 51. A valve, generally indicated at 52, is located at aforward end of the piston body 50 adjacent the recess 48. The valve 52is openable to enable communication between the recess 48 and a meltchamber 54 of the nozzle channel 22. The melt chamber 54 of the nozzlechannel 22 is located between the mold gate 24 and the valve 52. Whenthe injection piston 40 is in the retracted position and the valve pin28 is in the closed position, the volume of the melt in the melt chamber54 of the nozzle 18 is known. The known volume of melt in the meltchamber 54 corresponds to the volume of melt to be injected into eachmold cavity 26. The close proximity of the known volume of melt to beinjected and the mold cavity 26 reduces the amount of variabilityexperienced by prior art devices.

Referring to FIGS. 2–4, the valve 52 is better illustrated. The valvecomprises a flange 56 that extends outwardly from a lower end of thepiston body 50. As shown in FIG. 3, the flange 56 includes a series ofcutouts 58 that are spaced around the circumference thereof. A disc 66is axially movable relative to the flange 56. The disc 66 includes asecond series of cutouts 72 that are spaced around the circumferencethereof. The disc 66 is oriented so that the second series of cutouts 72is angularly offset from the series of cutouts 58 of the flange 56. Thedisc 66 and the flange 56 having the same outer diameter. Thisarrangement ensures that when the disc 66 abuts the flange 56, no meltcan flow past the valve 52 in either direction so that the desiredamount of melt, which is located in the melt chamber 54, is injectedinto the mold cavity 26.

The disc 66 further includes a stem 68 that extends outwardly therefromand an enlarged head 70 that is mounted on the end of the stem 68. Acentral cavity 60 is provided in the lower end of the piston body 50 toreceive the enlarged head 70 and limit the distance of travel thereof.The enlarged head 70 abuts a shoulder 62 of the central cavity 60 whenthe valve 52 is in the fully open position. The stem 68 is axiallymovable through a square-shaped bore 64 to reciprocate the disc 66 intoand out of engagement with the flange 56. The square shape is used toprevent rotation of the disc 66 with respect to the flange 56. It willbe appreciated that the stem 68 may be any shape or configuration thatprevents rotation of the disc 66, for example, the stem 68 may becircular with a groove for receiving a dowel. The disc 66 is movabletogether with and independent of the piston body 50 as a result of theforce exerted thereon by the melt in the nozzle channel. Retraction ofthe injection piston 40 causes the valve 52 to open by creating a gap 80between the flange 56 and the disc 66, and extension of the injectionpiston 40 causes the valve 52 to close by eliminating the gap 80. Otherarrangements may be used to provide a valve that performs the samefunction.

In operation, the pressurized melt stream flows through the manifoldbushing 16 to the manifold channel 14 of the manifold 12. Referring toFIG. 5, the cycle begins with the mold gate 24 in the closed position,in which the valve pin 28 engages the mold gate 24, and the injectionpiston 40 in the retracted position. In the retracted position, therecess 48 is aligned with the manifold channel 14 to receive melttherefrom. The melt flows from the manifold 12 into the recess 48, whichforces the valve 52 into the fully open position to allow melt to fillthe nozzle channel 22. Once the nozzle 18 is full of melt, the injectionpiston 40 is moved toward the extended position as indicated by arrow 82in FIG. 6. The forward movement of the injection piston 40 causes thedisc 66 to be forced toward the flange 56 to close the valve 52. At thesame time, the outer surface 51 of the piston body 50 shuts offcommunication between the manifold channel 14 and the nozzle channel 22.In this position, no additional melt can enter the melt chamber 54.Referring to FIG. 7, once the melt chamber 54 has been isolated from therest of the nozzle channel 22, the mold gate 24 is opened by retractingthe valve pin 28, as indicated by arrow 84. The forward stroke of theinjection piston 40, indicated by arrow 86, then forces the melt locatedin the melt chamber 54 of the nozzle channel 22 into the mold cavity 26,as shown in FIG. 8. The mold gate 24 is then closed by extending thevalve pin 28, as indicated by arrow 88 in FIG. 9, and the injectionpiston 40 returns to the retracted position, as indicated by arrow 90.This returns the injection piston 40 and valve pin 28 to the positionsof FIG. 5 so that the cycle can be repeated. As will be appreciated,this arrangement ensures that the volume of melt injected into the moldcavity 26 is equal for each mold cavity 26 and is constant for everycycle.

Referring to FIG. 10, another embodiment of an injection moldingapparatus 110 is shown. The numerals used previously in describing FIG.1 will be used again after raising the numerals by 100 where the partsto be described correspond to parts already described. The injectionmolding apparatus 110 is similar to the injection molding apparatus ofFIG. 1 with the addition of pressure sensors 200, 202 and 204, which areprovided in the mold cavity 126, the nozzle channel 122 and the manifold114, respectively. The pressure sensors 200, 202 and 204 sendinformation to the hot runner and mold controller 206 for use incontrolling the timing and sequence of movements of the injection piston140 and the valve pin 128. It will be appreciated that it is notnecessary to use all three pressure sensors 200, 202, 204. If desired,only one or two of the pressure sensors 200, 202, 204 may be used.

Temperature sensors 208 and 210 are provided to measure the temperatureof melt in the mold cavity 126 and in the nozzle 118, respectively. Anadditional sensor (not shown) may be provided in the manifold 112. Likethe pressure sensors 200, 202, 204, the temperature sensors 208, 210also send information to the controller 206 for use in controlling thetiming and sequence of movements of the injection piston 140 and thevalve pin 128. The controller 206 communicates with a motion drive 216that, in turn, communicates with position sensors 212 and 214. Theposition sensors 212, 214 are used to control the position and movementof the injection piston 140 and the valve pin 128, respectively. Thesensors may be of any known type, such as, for example, optical orinductive sensors. In some cases, only the position sensors 212 and 214may be used for the purpose of simplifying the injection moldingapparatus 110.

This arrangement is particularly useful in an injection moldingapparatus 110 in which all of the cavities have the same size. Thesensors 200, 202, 204 may be used to ensure that the pressure isgenerally equal in each of the mold cavities 126 and is generally equalbetween different batches of molded parts. The sensors 200, 202, 204 arealso useful in the case of a family mold, in which the pressure in eachmold cavity 126 is different and corresponds to a predetermined value.

Because a manifold typically supports more than one nozzle, it will beappreciated by a person skilled in the art that the movement of theindividual pistons of each nozzle may be staggered so that the pressurefrom the machine nozzle can remain constant.

In a further embodiment, the mold cavities 26 are of different sizes. Inorder to fill each mold cavity 26 properly, the melt chamber 54 of eachnozzle 18 must be sized to accommodate the correct volume of melt. Thenozzles 18 associated with each mold cavity 26 are identical; however,each injection piston 40 must be sized accordingly.

Although a preferred embodiment of the present invention has beendescribed, those of skill in the art will appreciate that variations andmodifications may be made without departing from the spirit and scopethereof as defined by the appended claims.

1. A hot runner injection molding apparatus comprising: a manifoldhaving a manifold channel; a nozzle, coupled to the manifold, having anozzle channel in fluid communication with the manifold channel, whereinthe nozzle is positioned within a nozzle bore of a mold cavity plate; aninjection piston extending through the nozzle channel of the nozzle; anda valve located at a forward end of the injection piston, wherein thevalve is selectively adjustable to block fluid communication between arecess, which is provided in the outer wall of the injection pistonupstream of the valve, and a melt chamber downstream of the valve withinthe nozzle channel.
 2. A hot runner injection molding apparatus asdefined in claim 1, further comprising: a mold gate disposed downstreamof the melt chamber; and a gating mechanism driven by an actuationmechanism and adapted to open and close the mold gate.
 3. A hot runnerinjection molding apparatus as defined in claim 2, wherein apredetermined volume of melt is located in the melt chamber of thenozzle channel when the gating mechanism is in a closed position.
 4. Ahot runner injection molding apparatus as defined in claim 2, whereinthe gating mechanism is a valve pin driven by a piston.
 5. A hot runnerinjection molding apparatus as defined in claim 2, wherein the valve isadapted to close when the injection piston is moved from a retractedposition to an extended position.
 6. A hot runner injection moldingapparatus as defined in claim 5, wherein the valve is adapted to openwhen the injection piston is moved from the extended position to theretracted position.
 7. A hot runner injection molding apparatus asdefined in claim 6, further comprising: a pressure sensor adapted tomeasure the pressure of the melt within the melt chamber; and acontroller connected to the pressure sensor, wherein movement of theinjection piston is controlled by the controller in response toinformation received from the pressure sensor.
 8. A hot runner injectionmolding apparatus as defined in claim 7, wherein the controller furtherreceives information from a temperature sensor.
 9. A hot runnerinjection molding apparatus as defined in claim 1, wherein a portion ofan outer wall of the injection piston abuts a portion of an inner wallof the nozzle channel.
 10. A hot runner injection molding apparatuscomprising: a manifold having a manifold channel; a nozzle, positionedwithin a nozzle bore in a mold plate, having a nozzle channel in fluidcommunication with the manifold channel; and an injection pistonextending through the nozzle channel of the nozzle, wherein theinjection piston includes, a piston body having an outer wall with anupstream portion abutting an inner wall of the nozzle channel, whereinthe outer wall includes a recess formed in a downstream portion of theouter wall, and a valve located at a forward end of the piston body, thevalve being selectively openable to allow fluid communication betweenthe recess and a portion of the nozzle channel downstream of the valve.11. A hot runner injection molding apparatus as defined in claim 10,wherein the injection piston is aligned within the nozzle channel suchthat movement of the injection piston to an extended position causes theupstream portion of the piston body to block fluid communication betweenthe manifold channel and the nozzle channel.
 12. A hot runner injectionmolding apparatus as defined in claim 10, further comprising: a moldgate disposed downstream of the melt chamber; and a gating mechanismdriven by an actuation mechanism and adapted to open and close the moldgate.
 13. A hot runner injection molding apparatus as defined in claim12, wherein the gating mechanism is a valve pin that extends through thepiston body.
 14. A hot runner injection molding apparatus as defined inclaim 10, wherein the recess in the downstream portion of the outer wallof the piston body is annular.
 15. A nozzle for a hot runner injectionmolding apparatus comprising: a nozzle body having a nozzle channel; aninjection piston extending within the nozzle channel, the injectionpiston including, a piston body having a recess in an outer wallthereof, and a valve located on a forward end of the piston bodydownstream of the recess, the valve being selectively closable to blockfluid communication between the recess in the outer wall of the pistonbody and a portion of the nozzle channel downstream of the valve.
 16. Anozzle as defined in claim 15, further comprising a gating mechanismextending through the nozzle channel.
 17. A nozzle as defined in claim16, wherein the gating mechanism is a valve pin selectively movable byan actuator.
 18. A nozzle as defined in claim 17, wherein the valve pinis slidably receivable within a central bore of the injection piston.19. A nozzle as defined in claim 17, wherein the piston body includes anupstream portion adapted to selectively block fluid communicationbetween a melt source and the nozzle channel.
 20. A nozzle as defined inclaim 15, wherein an upstream portion of the piston body has a firstdiameter and a downstream portion of the piston body has a seconddiameter that is less than the first diameter such that the recess inthe outer wall of the piston body is located in the downstream portionof the piston body and is annular.